UBC Theses and Dissertations

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UBC Theses and Dissertations

IPS e.max CAD and IPS e.max Press : fracture mechanics characterization Alkadi, Lubna T.


Objective: To determine fracture toughness (KIC) and fatigue crack propagation (FCP) parameters for IPS e.max CAD and IPS e.max Press. Materials and methods: For KIC determinations, 20 (6x6x6x12mm) notchless triangular prism (NTP) specimens of IPS e.max CAD and IPS e.max Press were prepared. IPS e.max CAD blocks were cut, ground and then crystallized, while IPS e.max Press ingots were pressed into molds obtained from wax prisms. Each specimen was mounted into a holder and custom grips were used to attach the holder to a computerized universal testing machine (Instron model 4301). The assembly was loaded in tension at a crosshead speed of 0.1mm/min and KIC was calculated based on the recorded maximum load at fracture. Fractured surfaces were characterized using scanning electron microscopy (SEM). The results were statistically analyzed using Weibull statistics and t-test (⍺=0.05). For FCP characterization, a pilot test was done with three Plexiglas NTP samples. A pre-crack was initiated in one of the specimen edges. Several lines were scribed on the side of the specimen to monitor crack propagation. The specimens were mounted in the holder and then attached to custom grips on a servo hydraulic fatigue-testing machine (Instron model 8511). A strain gauge was attached to these grips to monitor crack opening displacement. Each specimen was cyclically loaded in tension (Mode I) in a load range between 1 and 20 N and crack length was monitored and filmed using a high definition video recorder (SONY HDR-XR550V) attached to a microscope (Edmund Scientific Co, Barrington, NJ). Video recording was terminated once catastrophic fracture of the specimen occurred. Cyberlink Power Director and Image J software were used in data analysis. Results: KIC values were significantly higher for IPS e.max Press than IPS e.max CAD. The pilot FCP tests on Plexiglas revealed limitations with regards to the applicability of NTP specimen KIC test to FCP studies due to the presence of a trapezoidal crack front in the specimens. Conclusion: IPS e.max Press is superior to IPS e.max CAD in KIC. Further research should be conducted to evaluate the feasibility of using a trapezoidal crack front in FCP studies.

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